Changes in influenza viruses require regular reformulation of strain-specific influenza vaccines. Vaccines based on conserved antigens provide broader protection. Influenza matrix protein 2 (M2) is highly conserved across influenza A subtypes. To evaluate its efficacy as a vaccine candidate, we vaccinated mice with M2 peptide of a widely shared consensus sequence. This vaccination induced antibodies that cross-reacted with divergent M2 peptide from an H5N1 subtype. A DNA vaccine expressing fulllength consensus-sequence M2 (M2-DNA) induced M2-specific antibody responses and protected against challenge with lethal influenza. Mice primed with M2-DNA and then boosted with recombinant adenovirus expressing M2 (M2-Ad) had enhanced antibody responses that crossreacted with human and avian M2 sequences and produced T-cell responses. This M2 prime-boost vaccination conferred broad protection against challenge with lethal influenza A, including an H5N1 strain. Vaccination with M2, with key sequences represented, may provide broad protection against influenza A.

Pneumococcal surface protein A (PspA) and PspC of Streptococcus pneumoniae are surface virulence proteins that interfere with complement deposition and elicit protective immune responses. The C-terminal halves of PspA and PspC have some structural similarity and contain highly cross-reactive proline-rich (PR) regions. In many PR regions of PspA and PspC, there exists an almost invariant nonproline block (NPB) of about 33 amino acids. Neither the PR regions nor their NPB exhibit the alpha-helical structure characteristic of much of the protection-eliciting N-terminal portions of PspA and PspC. Prior studies of PspA and PspC as immunogens focused primarily on the alpha-helical regions of these molecules that lack the PR and NPB regions. This report shows that immunization with recombinant PR (rPR) molecules and passive immunization with monoclonal antibodies reactive with either NPB or PR epitopes are protective against infection in mice. PR regions of both PspA and PspC were antibody accessible on the pneumococcal surface. Our results indicate that while PspA could serve as a target of these protective antibodies in invasive infections, PspC might not. When antibody responses to rPR immunogens were evaluated by using flow cytometry to measure antibody binding to live pneumococci, it was observed that the mice that survived subsequent challenge produced significantly higher levels of antibodies reactive with exposed PR epitopes than the mice that became moribund. Due to their conservation and cross-reactivity, the PR regions and NPB regions represent potential vaccine targets capable of eliciting cross-protection immunity against pneumococcal infection.Pneumonia is the leading cause of mortality for children under the age of 5 years worldwide, and its most common etiology is Streptococcus pneumoniae (42). S. pneumoniae also cause otitis media and life-threatening meningitis. A 7-valent pneumococcal conjugate vaccine (PCV7) was introduced in the United States in 2000. PCV7 use reduced the number of cases of infections with vaccine capsular types in both immunized children (43) and nonimmunized individuals (18) in the same communities. But less than 5 years after the implementation of PCV7, reports of serotype replacement (increases in the number of invasive infections caused by strains of capsular serotypes not covered by the vaccine) began to appear (20,22,25,40). The observation of this serotype replacement within a few years after vaccine implementation and the fact that there are at least 91 capsular types (36) raise concerns about the long-term effectiveness of capsule-based vaccines and stress the need for continued development of effective, noncapsular serotype-dependent pneumococcal vaccines (2, 39).Surface proteins of pneumococci are important nonpolysaccharide vaccine candidates. Two of the more promising vaccine candidates are pneumococcal surface protein A (PspA) and pneumococcal surface protein C (PspC; also called CbpA). These two proteins have some similar structural features, and both proteins have ...

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The mechanisms of broad cross-protection to influenza viruses of different subtypes, termed heterosubtypic immunity, remain incompletely understood. We used knockout mouse strains to examine the potential for heterosubtypic immunity in mice lacking IgA, all Ig and B cells, NKT cells (CD1 knockout mice), or γδ T cells. Mice were immunized with live influenza A virus and compared with controls immunized with unrelated influenza B virus. IgA−/− mice survived full respiratory tract challenge with heterosubtypic virus that was lethal to controls. IgA−/− mice also cleared virus from the nasopharynx and lungs following heterosubtypic challenge limited to the upper respiratory tract, where IgA has been shown to play an important role. Ig−/− mice controlled the replication of heterosubtypic challenge virus in the lungs. Acute depletion of CD4+ or CD8+ T cell subsets abrogated this clearance of virus, thus indicating that both CD4+ and CD8+ T cells are required for protection in the absence of Ig. These results in Ig−/− mice indicate that CD4+ T cells can function by mechanisms other than providing help to B cells for the generation of Abs. Like wild-type mice, CD1−/− mice and γδ−/− mice survived lethal heterosubtypic challenge. Acute depletion of CD4+ and CD8+ cells abrogated heterosubtypic protection in γδ−/− mice, but not B6 controls, suggesting a contribution of γδ T cells. Our results demonstrate that the Ab and cellular subsets deficient in these knockout mice are not required for heterosubtypic protection, but each may play a role in a multifaceted response that as a whole is more effective than any of its parts.

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